clang_15: fix build!=(host==target) cross compilation

clang_15 appears to not cross compile in the build!=(host==target)
case due to two problems, which this commit fixes:

- It trips -Wmaybe-uninitialized on recent gcc, but only in the
  build!=host case (likely due to #ifdefs)

- Two more buildPlatform tools have been added:
  clang-tidy-confusable-chars-gen and clang-pseudo-gen

Co-authored-by: Rahul Butani <[email protected]>

pkgs/development/compilers/llvm/15/clang/default.nix

@@ -36,9 +36,14 @@ let
       "-DSPHINX_OUTPUT_MAN=ON"
       "-DSPHINX_OUTPUT_HTML=OFF"
       "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
-    ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    ] ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [
       "-DLLVM_TABLEGEN_EXE=${buildLlvmTools.llvm}/bin/llvm-tblgen"
       "-DCLANG_TABLEGEN=${buildLlvmTools.libclang.dev}/bin/clang-tblgen"
+      # Added in LLVM15:
+      # `clang-tidy-confusable-chars-gen`: https://github.com/llvm/llvm-project/commit/c3574ef739fbfcc59d405985a3a4fa6f4619ecdb
+      # `clang-pseudo-gen`: https://github.com/llvm/llvm-project/commit/cd2292ef824591cc34cc299910a3098545c840c7
+      "-DCLANG_TIDY_CONFUSABLE_CHARS_GEN=${buildLlvmTools.libclang.dev}/bin/clang-tidy-confusable-chars-gen"
+      "-DCLANG_PSEUDO_GEN=${buildLlvmTools.libclang.dev}/bin/clang-pseudo-gen"
     ];
 
     patches = [
@@ -60,6 +65,12 @@ let
 
     outputs = [ "out" "lib" "dev" "python" ];
 
+    env = lib.optionalAttrs (stdenv.buildPlatform != stdenv.hostPlatform) {
+      # The following warning is triggered with (at least) gcc >=
+      # 12, but appears to occur only for cross compiles.
+      NIX_CFLAGS_COMPILE = "-Wno-maybe-uninitialized";
+    };
+
     postInstall = ''
       ln -sv $out/bin/clang $out/bin/cpp
 
@@ -80,7 +91,7 @@ let
       patchShebangs $python/bin
 
       mkdir -p $dev/bin
-      cp bin/clang-tblgen $dev/bin
+      cp bin/{clang-tblgen,clang-tidy-confusable-chars-gen,clang-pseudo-gen} $dev/bin
     '';
 
     passthru = {

pkgs/development/compilers/llvm/git/clang/default.nix

@@ -36,9 +36,14 @@ let
       "-DSPHINX_OUTPUT_MAN=ON"
       "-DSPHINX_OUTPUT_HTML=OFF"
       "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
-    ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    ] ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [
       "-DLLVM_TABLEGEN_EXE=${buildLlvmTools.llvm}/bin/llvm-tblgen"
       "-DCLANG_TABLEGEN=${buildLlvmTools.libclang.dev}/bin/clang-tblgen"
+      # Added in LLVM15:
+      # `clang-tidy-confusable-chars-gen`: https://github.com/llvm/llvm-project/commit/c3574ef739fbfcc59d405985a3a4fa6f4619ecdb
+      # `clang-pseudo-gen`: https://github.com/llvm/llvm-project/commit/cd2292ef824591cc34cc299910a3098545c840c7
+      "-DCLANG_TIDY_CONFUSABLE_CHARS_GEN=${buildLlvmTools.libclang.dev}/bin/clang-tidy-confusable-chars-gen"
+      "-DCLANG_PSEUDO_GEN=${buildLlvmTools.libclang.dev}/bin/clang-pseudo-gen"
     ];
 
     patches = [
@@ -60,6 +65,12 @@ let
 
     outputs = [ "out" "lib" "dev" "python" ];
 
+    env = lib.optionalAttrs (stdenv.buildPlatform != stdenv.hostPlatform) {
+      # The following warning is triggered with (at least) gcc >=
+      # 12, but appears to occur only for cross compiles.
+      NIX_CFLAGS_COMPILE = "-Wno-maybe-uninitialized";
+    };
+
     postInstall = ''
       ln -sv $out/bin/clang $out/bin/cpp
 
@@ -80,7 +91,7 @@ let
       patchShebangs $python/bin
 
       mkdir -p $dev/bin
-      cp bin/clang-tblgen $dev/bin
+      cp bin/{clang-tblgen,clang-tidy-confusable-chars-gen,clang-pseudo-gen} $dev/bin
     '';
 
     passthru = {